Authority requirement cleanup

Pulled out some of the more basic requirements for authority to the top of the section.

The rest probably could still use some re-formating, but I suggest this is a useful step worth merging, since it pulls some important points to the top.
Rewrite of 4.1.3 Verb

As a sort of ‘clean slate decision' I left out references to previous
versions of the spec. I feel this has only a historic meaning to the
limited number of people that are aware of / were involved in previous
versions of the spec. In anyone feels this should be included, leave a
comment.

Possible confusion: The description of the ID property says a URI should
be human-readable. Yet, "tag:example.com,2012:xQr73H" is given as an URI
example a little earlier and that is not very human-readable. Is this a
contradiction?
Added: Reading guidelines for the non-technically inclined.

One of my intentions is to make this technical document as
'approachable' as possible for folks such as instructional designers,
project managers or even commercial people. To address them directly, I
added this little paragraph.
made this line more generic.
made some corrections based on Andrew's comments
Querying voided statements
Statement query changes

clarified that the multipart attachment format is to be used in responses when attachments are requested even if there are no attachments.
simplified existing query options while expanding them. (see extensive changes)
group filter updates, activity & group equality tweaks
targeted statement search clarificaton
Moved single-statement queries in to the main query parameter block in order to allow "attachments" and "format" to apply
added "voidedStatementId" to allow fetching voided statements
added "viewId" to allow limiting statement results on any pre-defined views the LRS provides
changes based on feedback

* returned SHOULD to MUST for including members in ad-hoc groups
* removed "viewId" query parameter
changes based on feedback
* made related_activities and related_agents behavior more specific
removed unclear example

as agreed with Andrew.
Based on feedback, reverted most group changes
* reverted all changes to group requirements to before this PR
* aside from impact on related_agent flag, and some "how to match on groups" clarifications, removed group query changes except to forbid anonymous groups as a filter option for agent parameter

Leaving prohibition of anonymous groups as a query parameter (and specificatoin that for an identified group specified
as a search parameter only the identifier is relevant) to avoid requiring LRS to search on a list of agents.
change based on feedback

* changed case of "subStatement" to "SubStatement" to be consistant
changes based on feedback
* added link to voided statements from voidedStatementId parameter
* added more detail to category description
missed that we already had a "voided" anchor
Formatting fix
minor fixes based on feedback

* removed apparently accidental suggestion that stored could be used in substatements
* added link to sub-statement query behavior in related voided requirement
* typo fix
removed some redundant language re: querying groups
Merge pull request #91 from paul-esch/master

rewrite of 3.1.4 Verb, and a small note to the not-so-technical readers.
Merge pull request #90 from bscSCORM/authority

Authority requirement cleanup
Update xAPI.md

Add vTrainingRoom to list of members of work group.